Process of recovering potash.



provements in f ARTHUR c. sran'cm or wss nmeron, msrmc'r or commune.

mosses or nncovmm e romsn.

Ne Drawing.

To all whom it may concern.

Be it known that I, ARTHUR C. SPENCER, a citizen of the United States, residing at Vvashington, have invented'certain new and useful Im- Processes of Recovering Potthe following is a specification.

ash, of which This invention relates to processes of recovering potash; and it comprises a method of recovering potash from alkali-bearing igneous rocks wherein'such rock .in a comminuted state is admixed with a limited quantity of lime, or equivalent calcareous material, such quantity being less than that required to form tricalcium compounds with the silica present and advantageously considerably less, the admixture is brought to a sintering or agglutinating temperature and the potash fumed off and recovered; all as more fully hereinafter set forth and as claimed,

Many igneous rocks contain compound silicates comprising potassium but the reof potash therefrom is somewhat covery being refractory diflicult, .these silicates and not yielding readily to reagents. This is particularly true of the feldspars, in which thereis, so to speak, an excess 'of silica. Such'rocks and minerals may however be treated to regain potash and form useful products by mixing with sufficient lime in the-fo-rmof limestone to form cem- ,e'ntitious products and then -furnacing in ways analogous to the ordinary cement-mak-.

ing operation, as by passing the mixture as a thin traveling stream down through a 1:0-

tary kiln against an opposed current of flame and flame gases (application Ser. No.

600,697). Under these conditions, the lime the alumina and'the.

unites with the silica, ferric oxid to form cement clinker of a character analogous to Portland clinker while the potash goes off in fume form and may be recovered with the kiln dust.

In making clinker analogous to Portland cement clinker however since there must be enough lime present to correspond to tricalcium compounds, of necessity large amounts of limestone must be employed. Taking an orthoclase of the normal composition, it requires. nearly three times its weight of 'limestoneto produce a normal clinker. With Portland cement, made from limestone and clay, roughly speaking there must be atleast twice as much limestone as clay. All this material must be heated to Specification of Letters Patent.

in the District of Columbia,

is the amount of fuel which must be used to bring the mixture to the desired heat and, consequently, the greater also is the amount of fire gases in and by which the potash fumed off is carried and diluted. And additional fuel, with concomitant products of combustion must also be used to supply the heat needed for the endothermic decomposition of calcium carbonate while the car bon dioxid driven ofl' adds to the volume oi effluent gases. There is some advantage however in performing the calcination by efiluent potassiferous gases since this reduces the temperature of the gases and renders easier the collection of fumes and particularly in using some types of fume collecting devices, such as the electrostatic fume depositors.

As the fumed offpotash must be recovered from the effluent gases, the high dilution of the fumes by the kiln gases in the described operation offers some practical difiiculties in the separation of the fumes for therecovery of the potash.

I have discovered that even with the highly siliceous'minera-ls like feldspar, the quantity of lime employed may be diminished with advantage so far as the recovery of potash is concerned; Instead of using" enough lime-to correspond with tricalcium aluminate and a considerable proportion of tricalcium silicate as in making Portland cement, less than that amount may be employed. with advantage. The clinkered products no longer have cementitious properties, in the. sense of being analogous to v Portland cement, but may be utilized for other purposes, as by' being converted into blocks, bricks, and other structural shapes by pressingor briqueting into form While the clinker is still hot and plastic. Being free of tricalcium silicate, the shapes are permanent and do not weather. The amount of lime may. go so-low as to be merely enough to constitute a moderate excess over the amount equivalent to the amount of potash present. In calculating the amount of lime to be added of course that contained in the original mineral may Patented Oct. 19, 1915.

Application filed January 6, 1912. Serial No. 669,748.

be'allowed for. For the present; purposesg".

.since thereis no effort to make anything like Portland cement, magnesla is equivalent,

molecule'for molecule, to lime and hereafter in using'the words calcium and lime? I desire them to be considered as equlvalent.-

fto magnesium and magnesia. .For'ex-.

ample, in' preparing the batch or charge, dolomitic lime may be used in lieu of ordinary lime. Similarly, the magnesia and lime in the mineral itself may be considered asequiva'lent. I have found that ordinarily win the. case of lowsilica rocks, theremay'be needed only 2 to 8-parts of total lime (or lime and magnesia) for every part of potash present in'the rock. In'case the batch comprises rock rather richin soda it is found that less lime is required to free the potash than to accomplish the same result in treating materials containing only potash or minor amounts of soda; Clinkering in the .presence of a large excess of lime liberates soda as Well as potash; bill, with less lime the sodaappears to be retained in silicate combina-tion withthe lime and the potash is liberated, the expulsion, of potash being ratio of 1.6 to 1. A ratio of about 1.5 :1 is

still better. Stated in another Way, the clinker or sinter advantageously contains less than 60 per cent. of lime (or lime and magnesia) and still more advantageouslyfor the present purposes, it will contain less than 58, or, better, less than 56 per cent.

' Using these small proportions of-lime, the

rock may be mixed in a finely divided state with the comminuted lime or limestone and the mixture brought to the sintering or fritting point, at which it is maintained for a sufiicient. time to allow a substantially complete expulsion of the potash as fumes. It is inadvisable to raise the temperature to the fusing point, since this lessens the surface exposed and thereby, concomitantly, lessens the evolution. of potash in a time unit. On the other hand, thetemperature should not fallbelow the softening point since otherwise the materials do not efi'e'ctively react.

While, as stated, the present process is applicable to the highlv siliceous rocks or mineralscontaining potash, such as orthoclase or potash feldspar, microcline, etc. I have foundthat it is particularly advantageous with the more neutral compound silicates of the leucite class and rocks containing them. Nephelite syenite andanalcite basalt carrying highsoda and potash are suitable mate- 'rials aswell as leucite and leucite rocks, such as leucite basalt. These feldspathoid si-licates do' not contain the large proportion of silica found in feldspar rocks. or in the mineral feldspar and are much more reactive, so that they are converted more readily with the small amounts of lime which are to be used in the presentinvention. And: of

course with the lower silicalcont'ent of feld- 'spathoid rocks and minerals, as comparedform basic calcium compounds.

'75- a with feldspathic, less lime is required to, There are many rocks whi'ch'are composed of, or contain large-amounts of, these feldspathoid minerals, such as many basalts'iand other 1 o. igneous rocks. Leucite basalts from Sweet'- -water, Wyo., carry 42 .to 54 per cent-of silica and 15 per cent. or. so sesquioxids, 10'

to '24 percent magnesia and lime, and 8*to 12 percent. potash. Rocksv of a"- similar range in composition are foun'd in many parts of. the country 'fand particularlv. in

to obtain other lowsilica'rocks With-6"to10 per cent. K 0. ,As arule these rocks carry low content of silica. Ilhave found that .WyOming and Montana. It is? not-difiicult these basalts and'relatedigneous rocks on. .mixing with small proportions of lime andholding at a sintering temperature for some time, readily give large yields ofpotash.

With the typical leucite basalts referred to above, I have-found that as little as 20 to 50: I

pounds-of added lime may be employed per 100 pounds 'of ore and .will give a copious evolution of potash. As stated, thisijma- .terialmay contain more than 20 per cent.- of

total magnesia andlime. Other materials may require even less. In practice a rock carrying 42 per cent. SiO and 15 per cent. R 0 (alumina and ferric oxid)-and con taining the equivalent in CaO and MgO of of from 10 pounds to. 70 pounds of lime, for each 100 pounds of rock, the latter amount being not enough to permit the formation of tricalcium silicate under clinkering con-- ditions. In case of 'a rock carrying 52 per 110. 25'per cent. 'GaO may require the addition cent. SiO and 12 per cent. R 0 With,1say,

15 per cent. of lime or its equivalent,.the

minimum aggregate of added lime required would be about 20 pounds, the maximum" permissible 100 pounds per .100 pounds of rock, and an advantageous addition of' lime would be from 80 to 90 pounds.

The sintering'operation may be performed in any apparatus adapted for direct heating of the batch or charge of reaction materials by flame gases. In order to carry off the fume it is necessary to have a moving body or current of vgases of some kind,-and this is conveniently and economically. afforded l then back.

5 use stationary kilns with briqueted material since less-free surface is afforded for the evolution and carrying away of fume from the material. Some gas movei'nent over the material is necessary and for this reason 3 electric heating is not advantageous unless special provisions be made for circulation of gas pver the sintering material, as by cyclic circulation of gas over the material through a fume condensing chamber and But, as stated, with the comparatively small proportions of lime and material used in the present invention, the volume of gases from the fuel used in firing is not excessive as it is where a high proportion of lime must be used as in the manufacture of ordinary Portland cement. Some gas current is necessary to carry the fume but it is not here necessary to use too much or an amount inconvenient for potash recovery, as in cement making operations.

The amount of fire gases passing over the material to carry away fumed oif potash may be still further reduced by bringing ,the material nearly to temperature in a so separate furnace and then. performing the sintering and potash recovery in a special furnace, as by using a pair of individually heated rotary kilns, the one feeding into the other. This expedient is particularly de sirable where limestone inlieu of lime is employed for furnishing the calcareous component. With limestone, the mixture may lee-calcined in a special kiln and then delivered to another kiln for the sintering and to fuming off of the potash. In this secondary kiln, the volume and movement of the gas current can of course be regulated to a nicety. It is however usually advantageous to use preleminarilycalcined lime in admixture with the powdered mineral matter instead of calcium carbonate. A very intimate mixture of the lime and the rock can be se cured by using milk of lime in the batch to form a slurry, This insures lime being in i contact with every portion of the rock and much lessens the time required for the fuming elf operation. However, dry mixtures of lime and *rock, though requiring somewhat longer time in the suitor-mg, work very Q satisfactoril in lieu of lime or limestone, other calcareous materials may be en'iployed. The objeet 1s to displace the potasuby lime at a'heat where the potash will fume oil". By using cal ium chlorid in lieu of or in conjunction with lime, the pota is converted into the coi'i'ipa'ratirely i'oiaiile form of potassium chlorid and the fuming o'll' requires less time ieraturc. The amount of calcium chlorid pd" may lie .doue at a soz'ueu'hut lower tem-v should ot be large enough to, be more than equivalent to the amount of CaO stated. A mixture of salt and lime may be similarly employed'since, as stated, with leucite and minerals of like character, there is greater tendency for soda than potash to be retained under the conditions of'the present operation. Where phosphate of. lime is available, it may be used, or. gypsum may be employed. If sulfur is present in the fuel sulfate of potash is formed in the fume. Sulfur burns to sulfur dioxid andtrioxid which combine with the potash of the fume, forming sulfate.

The rock used may he disintegrated to any extent desired but advantageously it is in very fine powder. The finer, the less the time required in the fuming of? operation.

It is advantageous to use sulficient lime, (or equivalent calcareous material as explained) to about balance the silica, alumina, and iron sesquioxid. of the material in bimolecular proportions, or at least an amountin excess of double the chemical equivalent of the silica present, using ordinarily a slight excessabove this amount but not reaching the tricalcium silicate ratio. There may be advantageously enough lime to form a bicalc ium silicate with the silicate of the rock, and enough to form tricalcium compounds with the alumina and iron sesquioxid prescut, but not enough to form any substantial amount of tricalcium silicate, with the silica present. After making an intimate mixture of tne lime (and lime is much preferable to limestone for the present purposes) with the rock, the mixture is to be sintered and maintained at a high temperature for a sufficient length of time to allow as complete an evolution of the potash aspossible. The evolution of potash in a time unit is substantially proportional to the surface exposed and it is therefore advantageous, as stated, to keep the mixture below the actual fusing point and at the sintering point. A full red heat is a desirable temperature if continued for a sufficiently long time. higher temperature has however been found advantageous, quickeningthe evolution of the" fumes, provided the. temperature does not reach the melting point. hiuch depends on the particular rock.

While, as stated, any convenient type of "combi'istion heated furnace may beemployed The sintered but unfused. material deuniting by a welded'union at their meeting surfaces to produce an open textured strong aggregate useful for structural purposes.

Ordinarily there is rather less lime than mineral used in employing the stated proportions.- This means that, in bringing to and maintaining at the sintering temperature, much less fuel is required than would be necessary in making cement ,from the same rock; and the dilution of the fume is correspondingly diminished. The operation thus gives a comparatively concentrated fume which can .be readily treated in any of the ordinary types of fume recovering apparatus. The dust and fumiform products of the furnace or kiln may be taken up in suspension by the gases which pass therethrough. These products may be collected by means of a flue and passed through settling chambers or dust catchers which may be of any convenient type. lVith certain types of dust traps, it is advantageous to provide water cooled surfaces within the chambers to promote the desired settling of the potassiferous fume. Of course gas Washers of different types may be employed to effect the separation of the potash produclt from'the gases which carry it out of the kin. i

I do not describe in detail apparatus for carrying out my process as it is sufficiently obvious that furnacespr kilns like those now used in other arts are adapted for the treatment here described. If certain types of kilns are used it will be necessary to form the materials of the batch into briquets prior to the heat treatment, but this procedure which, for reasons stated, is little advantageous, cannot constitute a departure from my invention which resides in the advantageous proportioning ot' the charge batch, permitting evolution of alkali at a relatively low temperature. reducing the required consumption of fuel, and promoting the ready collection of the alkali products.

- \Vhat I claim is:

1. In the treatment of igneous rocks and minerals carrying potash and silica, the process of recovering potash which comprises heating and maintaining the same at a sintering temperature in the presence of lime in amountat'least sullicient to replace.

said potash and to form dicalcium silicate.

but not enough to form tricalcium silicate after providing for tricalcium aluminate and tricalcium ferrite} such temperature being maintained until substantially all the potash is removed and recovering the pot ash fumed oil" in the sintering.

2. The process of recovering potash from igneous rocks characterized f eldspathoid minerals which comprises heating and maintaining the same in' a comminuted form and admixed with calcareous material at a sintering temperature, the amount of such calcareous material being. at least suflicient to replace the potash present and to form dicalcium silicate but insuiiicient to form tricalcium silicate with the silica present after required to form'dicalcium compounds with acidic bodies present and such-temperature being maintained until substantially all the potash is removed, and recovering the pot- 1 ash fumed ofi 1n the sintermg.

4. The process of recovering potash from igneous rocks carrying potash in silicate combination which comprises clinkcring a GOIIllI'lllllltBd mixture of the rock with calcareous material till substantially all the potash is fumed on, said mixture being pro portioned to yield clinker containing at least 1.87 times as much lime as. silica but less than 1.7 times as much lime as silica plus alumina plus iron oxid. I

5. The processof recoveringpotash which comprises sintering a comminuted mixture ofdime and rock comprising fcldspathoid minerals so proportioned that there is snl'licient lime equivalent to make Al O 3CaO and Fe O LiCaO with the alumina and iron oxids present but not suiiicient to yield any substantial amount of Si(). ,3(a0.

(3. The process of recovering potash which comprises slntering a commniuted mixture of lime and rock comprising feldspathoid minerals so proportioned that the resulting clinker may show on analysis less than 1.7 timesas much lime as the total of SK) and but at least 1.87 times as much lime as silica.

7. The process of recoverin g potash which comprises,sintering a comm-muted mixture of lime and rock comprising feldspathoid times as much lime as the total of SiO and R 0 but atleast 1.87 times as much lime silica. e

9. The process'of recoverinn' potash which comprises sintering a oomminutecl mixture of lime and rock comprising feldspathoid minerals so proportioned that the resulting clinker may show on analysis less than 60 per cent. of lime.

10. The process of recovering potash than 5% pewhich comprises sintering a comminuted mixture of lime and rock comprising fel spatlioid minerals so proportioned that the resulting clinker may show on ei izilysis less than 58 per cent. of lime.

11. The process of recovering potash which comprises sintering a commimitecl fioplesof this patent may be obtained for five cents e SIssms, Iii-01 35202:

Washington, D, G. 

